This invention relates generally to vehicle tire analysis and more specifically to a method and apparatus for improving the accuracy, efficiency, and reliability of analyzing tire tread patterns and the contact areas produced by such patterns under various static and/or dynamic conditions.
In the manufacture of vehicle tires, tread design is of particular significance as it translates into vehicle handling characteristics under various road surface conditions. This being the circumstance, various methods of tread analysis have been developed to investigate tread pattern effect as it relates to tread contact area under several conditions, one particular being hydroplaning on a wet road surface.
One of these methods involves placing the tire in a tire deflection machine and applying various static loads to the tire to obtain a deflection "footprint" of the tread contact area. In this respect, the tread is painted and placed on a contrasting surface such that a high contrast image of the deflected tread pattern is produced. The image is then compared to a reference image by a visual comparison or by an actual measurement of the contact areas of the image.
Another of these methods is generally known in the industry as aquaplane photoanalysis. This method involves photographing a tire "footprint" as it traverses a wet glass plate. The plate is generally covered with a colored fluid to aid in photo contrast, and high speed color photographs are taken through the glass plate as the tire travels over it at a specific speed. Upon developing the film, a color photopositive print is obtained with the tread contact area being defined by black areas while all other areas are defined by the color of the fluid on the plate. Thus, the photograph provides a means for analyzing the ability of the tire to maintain road surface contact under various water versus speed conditions.
Techniques for analyzing these photographs involve comparing a reference print which represents 100 percent tread contact area to the dynamic print that is usually something less than 100 percent contact area depending upon the ability of the tread pattern to "shed" water. In one technique of evaluating aquaplane photographs, the tread contact areas are manually integrated by tracing a planometer around the border of the black areas. This measurement is compared with a similar measurement taken on a static photograph of the same tread pattern. Another technique involves placing the dynamic photopositive print over the static or reference print and visually comparing, block by block, the tread contact areas of the two prints.
Thus, the present methods of tire tread analysis are essentially human oriented and, therefore, suffer some distinct disadvantages. For example, the accuracy of integrating the tread contact area is limited by the ability of the individual to distinguish the black versus color boundary. Furthermore, being a manual operation, each tread "footprint" takes approximately 20 to 30 minutes to integrate depending upon the amount of contact area to cover and the accuracy of the measurement desired. Naturally, a more painstaking measurement will result in greater accuracy but at the expense of increased time. This being the circumstance, the number of tests that may be analyzed or evaluated for each tread design is time limited and the cost per test becomes a matter of concern.
In view of these disadvantages, it is apparent that a need exists for a more accurate, reliable and efficient method of tire tread pattern analysis. It is accordingly among the principal objects of the invention to provide a method and apparatus for analyzing tire tread contact area images that avoids the disadvantages of the prior art, yields reliable results, and is a quick and automatic operation.
Generally, the principal object and other objects and advantages are achieved by providing a method and apparatus in which the high contrast black and white images are produced of the tire tread contact area in static and/or dynamic condition. The tread contact image is illuminated and optoelectronically converted to an electrical signal such that a comparison may be made between it and a reference representative of a control base tread contact condition. The comparison results in a readout useful in an analysis of tire tread pattern effect.